In recent years, the issue of global warming has been attracting attention amid growing interest in environmental problems. Global warming develops as greenhouse gas concentrations are raised in the atmosphere. Greenhouse gases such as carbon dioxide, methane, and perfluorocarbons (PFCs) have strong absorption in the infrared region, and when they are released into the air, they absorb the energy radiated from the Earth's surface and give off a part of the energy to the underlying Earth's surface. Namely, a part of the energy given off from the Earth's surface is returned to the Earth's surface by greenhouse gases, and the so-called greenhouse effect causes global warming.
In the 3rd Conference of the Parties to the UNFCCC, which was held in 1997, the greenhouse gas reduction targets were set for developed countries, and it was decided to reduce certain levels of greenhouse gases between the years 2008 and 2012, on the basis of the levels in 1990. The assessment of the greenhouse effect of greenhouse gases based on the volume of greenhouse gases and their global warming potentials shows that carbon dioxide is the biggest contributor to the greenhouse effect, followed by methane. Particularly, methane (global warming potential: 21) is higher in global warming potential than carbon dioxide (global warming potential: 1) and even a small amount of methane greatly affects global environment. Against these backgrounds, there is a strong demand for a technique to inhibit methane production.
In general, methane is produced through methane fermentation carried out by methanogenic bacteria (methanogens), and in the environment, methane is known to be produced chiefly from the ruminant stomach (rumen) and paddy fields. Methanogens synthesize methane under anaerobic conditions. In the ruminant stomach, organic acids are produced in the phase of the digestion of grass and the like and the organic acids are converted into methane by methanogens. In paddy fields, methanogens decompose organic substances such as rice stubble to produce methane. The methane derived from ruminants and paddy fields is reported to account for 20-30% of the total methane, and if the methanogenesis in these sources can be inhibited, methane, which is a greenhouse gas, can be reduced to a great degree.
The techniques to inhibit methanogenesis which have been reported so far are methods such as use of cysteine (Patent Document 1) and use of lactic acid bacteria and the like (Patent Document 2).
CITATION LIST
Patent Document
Patent Document 1: JP H07-322828 A
Patent Document 2: JP 2009-201354 A